Only a few prior art patents have taught the immobilization of lead in different kinds of wastes to make the treated residuals suitable for disposal as special waste in a RCRA approved and licensed landfill facility. For example, some known methods to treat broader groups of metals are shown in U.S. Pat. No. 4,149,968 to Kupiec et al., U.S. Pat. Nos. 4,889,640 and 4,950,409 to Stanforth, U.S. Pat. No. 4,701,219 to Bonee, U.S. Pat. No. 4,652,381 to Inglis, and U.S. Pat. No. 4,671,882 to Douglas et al.
Kupiec et al. teaches the immobilization of heavy metals by treating an alkaline slurry of waste with a mixture of bentonite clay and Portland Cement.
Stanforth teaches a method of treating solid hazardous waste (containing unacceptable levels of lead and cadmium) with reactive calcium carbonate, reactive magnesium carbonate and reactive calcium magnesium carbonate. The patent teaches that addition of water is beneficial to facilitate the mixing of the solid waste with treatment additive and conversion of lead into non-leachable forms. Stanforth further discloses mixing solid waste with lime and carbon dioxide or bicarbonate.
Bonee U.S. Pat. No. 4,671,882, discloses the treatment of spent sorbent wastes (containing leachable vanadium, nickel, and sodium) with alkaline earth metal compounds, including calcium sulfate. According to that patent, powdered lime (calcium hydroxide or calcium oxide) and calcium fluoride were most effective in decreasing the leachable vanadium and nickel.
Bonee discloses that calcium chloride, calcium carbonate, gypsum and sodium carbonate are relatively ineffective at reducing the leaching of vanadium and nickel from a petroleum cracking process particulate waste.
Douglas et al. discloses a process for producing a non-hazardous sludge from an aqueous solution by addition of phosphoric acid or an acid phosphate salt, adjusting the pH to about 5, adding a coagulating polymer and raising the pH to above 7 through the addition of lime. Then, the process includes dewatering the resulting sludge. This constitutes at least 5 or more steps making it cumbersome, time consuming and expensive.
Inglis teaches a process of treating industrial wastewater which has a pH of 2 and which is contaminated with sulfuric acid, lead, cooper and zinc. Calcium carbonate is added along with air to wastewater. This results in neutralization and formation of insoluble metal salts. The process is not applicable to wastes that have a pH of 6 to 9. However, limestone is relatively ineffective in removing lead from hazardous, solid or sludge material. Limestone does not react in the solid materials and metal carbonates that are formed are subject to degradation by acid rain and acidic landfill leachate conditions.
Hazardous wastes containing excessive amounts of leachable lead are banned from land disposal. The regulatory threshold limit under Resource Cons. and Recovery Act is 5 mg/l of leachable lead as measured by TCLP (toxicity characteristic leaching procedure) test criteria, United States Environmental Protection Agency (USEPA) method 1311 (SW-846). Waste materials containing TCLP lead levels in excess of 5 mg/l are defined as lead-toxic hazardous waste and are as such restricted from land-filling under current land ban regulations. The cost of disposing lead toxic hazardous waste materials is in excess of $200.00 per ton plus the cost of transporting the hazardous material to landfills for hazardous wastes, which do not exist in every state. This makes the disposal of lead toxic hazardous waste material very expensive. Therefore, treating the lead-bearing process materials and waste streams to render them non-hazardous by RCRA definition would cut down the costs of transportation and disposal tremendously.